The invention generally relates to screw compressors. More specifically, the invention relates to positioning an internal pressure relief valve in a screw compressor.
A screw compressor, in addition to a condenser, an expansion device, and an evaporator, is a key component of a refrigeration system. The screw compressor includes a common housing, hereinafter referred to as a ‘rotor case’, in which a primary helical rotor is intermeshed with at least one secondary helical rotor. The primary helical rotor is driven by an electric motor. Due to the intermeshing between the primary and secondary helical rotors, the secondary helical rotor is driven in counter-rotating motion by the rotation of the primary helical rotor. The function of the primary and secondary helical rotors is to compress a refrigerant entering the screw compressor in a gaseous state, hereinafter referred to as a ‘refrigerant gas’. A refrigerant is a medium of heat transfer that produces a refrigeration effect by absorbing and dissipating heat in the refrigeration system. The refrigeration effect refers to the amount of cooling produced in the refrigeration system. The refrigerant gas enters the rotor case through an inlet port and gets trapped between the inner walls of the rotor case and grooves of the primary and secondary helical rotors. Due to the constant rotary motion of the primary and secondary helical rotors, the refrigerant gas gets compressed and is discharged through a discharge port. The compressed refrigerant gas then enters the condenser under high pressure. In the condenser, the refrigerant gas is cooled and thereafter liquefied by heat exchange with the air or water present in the condenser. Thereafter, the resulting refrigerant liquid is expanded in the expansion device and is brought down to a low pressure and temperature. The low pressure, low temperature refrigerant liquid is then supplied to the evaporator. In the evaporator, the refrigerant liquid absorbs the heat present in the evaporator and changes into gaseous state, thereby cooling the refrigeration system. Subsequently, the refrigerant gas leaves the evaporator and undergoes compression in the screw compressor, thus completing a refrigeration cycle.
To vary the refrigeration effect, the compression capacity of the refrigeration system needs to be controlled. The compression capacity refers to the volume of compressed refrigerant gas discharged from the screw compressor. The compression capacity is proportional to the refrigeration effect in the refrigeration system. In order to control the compression capacity, the rotor case of the screw compressor is provided with a slide valve. The slide valve controls the compression capacity by varying the volume of the refrigerant gas in a working chamber. The working chamber is defined by the inner walls of the rotor case of the screw compressor. This allows only the required volume of refrigerant gas to be compressed and discharged from the screw compressor.
During the process of compression, an over-pressure situation may arise in the screw compressor. During the over-pressure situation, the internal pressure of the screw compressor exceeds the maximum allowable internal pressure. This can cause damage to the screw compressor. In order to relieve excess internal pressure, an internal pressure relief valve is provided in the screw compressor. The internal pressure relief valve vents the excess internal pressure from the discharge side (high-pressure side) to the suction side (low-pressure side) of the screw compressor, thus preventing damage to the screw compressor.
FIG. 1 illustrates a view of a conventional screw compressor 100 with its components. Screw compressor 100 includes a rotor case 102, a slide valve supporting member 108, a slide valve 110, and two internal pressure relief valves 112a and 112b. Rotor case 102 accommodates a primary helical rotor 104 and a secondary helical rotor 106. Primary helical rotor 104 and secondary helical rotor 106 together compress the refrigerant gas in rotor case 102. Conventionally mounted internal pressure relief valves 112a and 112b take up a lot of space in screw compressor 100. Further, when the size of screw compressor 100 increases, either the size of internal pressure relief valves 112a and 112b have to be increased accordingly, or more internal pressure valves have to be accommodated in rotor case 102 of screw compressor 100. As a result, the amount of casting material required to manufacture rotor case 102 increases, thereby increasing the overall size, weight, and manufacturing cost of screw compressor 100.
In light of the foregoing discussion, there exists a need for an apparatus that relieves excess internal pressure in a screw compressor, without taking up any additional space, even when the size of the screw compressor is increased or multiple internal pressure valves have to be accommodated. Further, the apparatus should be arranged such that any extra amount of casting material or additional cost of manufacturing the rotor case of the screw compressor is avoided.